1. Field of the Invention
The present invention relates to a mechanism for driving a carriage and, more particularly, to means for mounting a follower which is carried on the carriage for engaging with the guide groove of a drive shaft.
2. Description of the Prior Art
For example, a floppy disc drive is equipped with a carriage for driving a magnetic head, which is made operative to record data in a floppy disc and to read out the data from the floppy disc, to a desired track on the floppy disc in accordance with the operation of the operator.
Before entering into detailed description of the invention, specific review will be made upon the relevant prior art with reference to the accompanying drawings. FIGS. 5 and 6 are schematic views showing the carriage driving mechanism of the above-specified type known in the prior art.
In these Figures: reference numeral 1 indicates a drive shaft which is formed with a helical guide groove 1a in its outer circumference; numerals 2 and 3 indicate bearings which bear the drive shaft 1; numeral 4 indicates a motor for driving the drive shaft 1; numeral 5 indicates a gear train for transmitting the driving force of that motor 4 to the aforementioned drive shaft 1; numeral 6 indicates a carriage; numeral 7 indicates a magnetic head which is carried on the carriage 6; numeral 8 indicates guide shafts for guiding the carriage 6 in a direction parallel to the aforementioned drive shaft 1; and numeral 9 indicates a follower which is carried on the aforementioned carriage 6 for engaging with the guide groove 1a of the aforementioned drive shaft 1.
The drive mechanism thus constructed alternately switches power supply to the magnetization phases of the motor 4 to intermittently turn the drive shaft 1 thereby to intermittently drive the carriage through the follower 9 in the directions of arrows A and B along the guide shafts 8 so that it can carry the magnetic head 7 to a predetermined recording track of the floppy disc.
As the drive shaft to be used in the drive mechanism of this kind, the present applicant has previously devised the drive shaft, which has its helical guide groove 1a formed at a predetermined angle of rotation with portions 1b having a zero angle of lead .theta., as shown in FIGS. 7 and 8, and described in utility model registration (i.e., Japanese Utility Model Application No. 57-187126).
The carriage driving mechanism using the above drive shaft 1 drives the carriage 6, i.e., the magnetic head 7 to the predetermined position, even if the angle of lead .theta. of the guide groove 1a is more or less dispersed or if a small-control error is caused in the revolutions of the motor 4, so that it can prevent in advance the erroneous tracking.
In the driving mechanism of this kind according to the prior art, however, since the follower 9 is fixedly mounted on the carriage 6, the following disadvantages are caused in case the drive shaft 1 shown in FIGS. 7 and 8 is used:
(1) Since the guide groove 1a is not formed into a smooth circumference, as is apparent from FIGS. 6 and 7, the contacting pressure between the follower 9 and the guide groove 1a fluctuates in accordance with the revolutions of the drive shaft 1 to obstruct the smooth sliding of the follower 9 in the guide groove 1a. More specifically, if the follower is set in advance in a position to abut against the bottom 1c of the guide groove 1a, the contacting pressure between the drive shaft 1 and the follower 9 becomes excessive when the drive shaft 1 revolves to a position in which the follower 9 abuts against the transition 1d of the guide groove 1a, so that the frictional force makes the operation of the carriage 6 lack smoothness. Moreover the drive shaft 1 and the follower 9 become liable to be worn and not only degrade remarkably the durability of the carriage driving mechanism but also allow fine dust particles from the drive shaft 1 and the follower 9 to adversely affect the floppy disc.
(2) In order to smooth the sliding movement on the guide shafts 8, moreover, the carriage 6 is formed, as shown in FIG. 6, with a guide shaft receiving hole 6a having a larger diameter than that of the guide shaft 8. As a result, if the contacting pressure between the drive shaft 1 and the follower 9 fluctuates in accordance with the revolutions of the drive shaft, the carriage 6 becomes liable to pitch thereby to invite disadvantages that noises are made and that the durability is degraded.
(3) If the follower 9 is set in advance in the position to abut against the transition 1d of the guide groove 1a so as to avoid the excessive contacting pressure between the drive shaft 1 and the follower 9, a gap is established inbetween the bottom 1c of the guide groove 1a so that a backlash is caused between the guide groove 1a of the drive shaft 1 and the follower 9, in case the revolving direction of the drive shaft 1 is reversed, thereby to make it impossible to drive the carriage 6 to an accurate position.